Porous plate developer for thermally sensitive film



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POROUS PLATE DEVELOPER' FQR THERMALLY SENSITIVE FILM Filed Feb. 8, 1968IN VENTOR. BY gen/e 5 6*. z 0N0! wz zwww United States Patent 3,496,332POROUS PLATE DEVELOPER FOR THERMALLY SENSITIVE FILM George G. Lunde,White Bear Lake, Minn., assignor to Minnesota Mining and ManufacturingCompany, St. Paul, Minn, a corporation of Delaware Filed Feb. 8, 1968,Ser. No. 704,131

Int. Cl. H051) 1/00 US. Cl. 219216 3 Claims ABSTRACT OF THE DISCLOSUREApparatus for uniformly developing an image-exposed intermittentlyadvancing continuous strip of radiationsensitive heat-developable filmby drawing the film between porous plate diffusers of low pressureheated air includes means for retracting said plates upon stoppage ofthe film and for controllably delaying the forward motion of said filmafter returning the plates to operative position.

This invention relates to apparatus and method for use in thedevelopment of visible images in image-exposed radiation-sensitiveheat-developable sheet or film strip materials.

A type of radiation-sensitive thermally developable strip material whichis particularly useful for making a visible record of transientelectronically produced latent images has a sensitive coating comprisinga combination of photosensitive silver halide and light-stable organicsilver salt in conjunction with a reducing agent, a described, forexample in US. patent application Ser. No. 693,714. The sensitivecoating is soft and subject to abrasion. Thermal development to auniform end-point requires careful control of both time and temperatureof heating and is particularly difficult to achieve in a systemrequiring frequent or occasional discontinuous movement of the exposedstrip.

Thus, exposure of the advancing strip to contact with heated air in anoven results in over-development of that portion of the strip remainingwithin the oven during periods of stoppage. Contact with smooth heatedmetal platens or drums produces a similar problem. Attempts to cool theoven or to lift the strip from the metal surface during stoppage periodsare ineffective due to the inherent heat capacity of the strip, thedifiiculties in obtaining uniform full contact with heated surfaces, andother problems.

It has now been found possible to achieve fully uniform development ofintermittently advancing exposed radiation-sensitive heat-developablestrip materials of the type hereinbefore described by heating the stripwith heated air applied smoothly over one or both of the strip surfacesfrom retractable porous diffuser elements. The process may be carriedout in a manner now to be described in conjunction with the appendedschematic drawing which illustrates in elevation and partly in section apresently preferred embodiment of apparatus applicable to thedevelopment of a normally smoothly continuously advancing narrow stripof sensitive film.

In using the apparatus, which is enclosed within suitable cabinets, notshown, a strip of sensitive film 10 from supply reel 11 is drawn througha first vacuum buffer station 12, past an exposure station 13, andthrough a second vacuum buffer station 14 before progressing to thedeveloping unit indicated generally at 15. The film advances from thestation 12, past the station 13, and to the station 14 in anintermittent manner, i.e. one frame at a time, under the force suppliedby friction drive wheels 16 and 17 which are operated in synchronism.Exposure may be with a light-image supplied by suitable opticalequipment, or by any other desired means. A presently preferred exposuresource employs a modulated electron beam operating in a vacuum chamberthrough whlch the film is passed by means of suitable vacuum ports asindicated in the drawing. As an example, from two to six 16 mm. framesmay be exposed per second, thus requiring a rate of advance of the filmof about three to about ten cm./sec. The two vacuum buffer or storagestations provide for smooth flow of film from the supply reel and to thedeveloping unit while maintaining uniform tension on the interveningsegment of film.

The film is fed to the developing unit by pull drum 18 and passes aroundidler roll 19, between platens 20 and 21, between ducts 22 and 23,through a third vacuum buffer station 24, past a viewer station 25, andfinally to windup reel 26. Uniform tension on the film is supplied bythe vacuum buffer station, from which the film is mtermittentlywithdrawn by the windup reel 26, the action being controlled by opposingswitch contacts 52, 53. Random inspection is permitted at the viewerstation while the film is at rest.

The two platens 20, 21 are identical and, as illustrated for platen 20,comprise a back wall 27 and sides 28 forming a plenum chamber 29 whichis closed with a porous face plate 30. A coil of resistance wire 31 iswound around a ceramic supporting rod 32 which is itself fastened withinthe chamber 29 on supporting frames 33. Electrical connection with thecoil is established through contacts 34, 35. Air under low positivepressure enters the chamber 29 through one or more ports 36 in wall 27,is heated through the agency of the coil 31, and flows from the chamberthrough the porous plate 30 which is itself thereby heated and assures auniform temperature in the issuing air. The temperature of the plate issensed by a thermocouple 37 appropriately embedded in the plate 30 andis controlled to the desired level by regulation of the power input tothe coil 31.

In an illustrative embodiment useful in developing the 16-II1II1. filmreferred to hereinbefore, the porous plate 30 is a fiat smooth-surfacedsection of fine porous bronze filter plate measuring x 1% x 24 incheswhich passes approximately ten cubic feet of air per minute per squarefoot under the applied pressure differential of two inches of water andat a temperature of C. The coil 31 is made of No. 22 gage Nichrome wireand has a resistance of 35 ohms. Plate temperatures within the range ofup to about 200 C. may easily be maintained with variations of less thanone degree.

The platens 20, 21 are supported on the frame by movably mounted supportlinkages 38-41 as shown and in position for movement toward and awayfrom each other under the action of connecting links 42, 43, 44 andhydraulic cylinder 45, the platen faces remaining parallel to each otherat all times. Support 40 and link 44 are each keyed to a commonrotatably supported shaft 50. The application of pressure to thecylinder 45, through air entry port 46, forces the platens toward eachother and into close proximity with the flat surfaces of the strip 10,which is then uniformly heated by the warm air flowing from the porousplates 30. Under conditions of constant rate of advance of the strip,and with proper adjustment of temperature and air flow, development ofthe exposed strip proceeds with complete uniformity.

If for any reason the movement of the strip 10' must be halted, as forexample when data input is curtailed or a correction must be made, athree-way valve 47 simultaneously is actuated to permit the piston ofthe hydraulic cylinder 45 to return to closed position, under thepressure of the spring 51 thereby promptly separating the platens 20 and21. In the example given, the platens are each removed to a distance ofapproximately inch (about 2 cm.) from the interposed strip of film.

The rapid retraction of the platens, combined with the low rate of flowof the heated air through the porous plates and the presence of anadequate volume of cooler air surrounding the area, results in a rapidcooling of the film strip to a temperature at which further developmentis effectively prevented. An examination of the strip at this point willshow complete image development at the point of exit from between theplatens, changing gradually to a condition of initial visibledevelopment at a point approximately midway between input and exit. Ifnew the platens be brought into developing position and movement of thestrip resumed, it will be found that a portion of the strip firstissuing from the development area will be inadequately developed. Toovercome this difficulty there is provided a time delay relay 48 in thefilm drive circuit. Closing of the starting switch 49 then promptlyactuates the solenoid valve 47 to return the platens to the developingposition closely adjacent the strip, but the operation of the pull drum18 and the advancement of the strip is delayed by the relay 48 for acontrollable period of time, usually about one second, sufficient topreheat the enclosed strip to a degree such that all parts of the stripwill be evenly and uniformly developed.

Cool air is supplied to the interior of the cabinet and to the spacesurrounding the unit through opposing ducts 22, 23 and directly onto thestrip of film as it issuesfrom beetween the platens 20, 21, therebyimmediately terminating the development reaction as well as providingfor rapid cooling of the strip upon separation of the platens in themanner described.

Where a single retractable heating platen is to be used, cooling may ifdesired be provided simultaneously at the reverse surface of the sheetfrom a similar porous plate supplied with cool air, and additionalcooling platens may be positioned adjacent either or both surfaces ofthe sheet as it is removed from the heating area.

In place of smooth continuous advance through the developing station,the strip may be subjected to frameby-frame or other regularintermittent advance motion but at an over-all constant rate, forexample by means of a Geneva drive as employed for cinematographicexposure and projection. During such regular intermittent advance theheating platens will remain in position closely adjacent the film; butany delay in the over-all constant rate of advance will call for promptretractionof the platens. The same principle may be extended to thesituation wherein only a single frame or segment or sheet of sensitivematerial is to be developed at a time, with prompt retraction of theheating platen or platens and cooling of the sheet on completion ofdevelopment, followed by removal of the developed sheet and insertion ofa next following sheet. Particularly in such instances the use of asingle heating platen adjacent the sensitive surface, in conjunctionwith an opposing cooling platen adjacent the back surface of the sheet,is found desirable.

It will be understood that the apparatus suitable switches, vacuum andpressure pumps, means for regulating and controlling temperatures,pressures, speeds and other variables, means for connecting to suitwillinclude able power supply, and other auxiliary equipment, not shown forreasons of clarity and simplicity. It will further be understood thatequivalent but specifically different components may be substituted forthose here described and illustrated in obtaining substantially the sameresults in substantially the same way without departing from the spiritof the invention.

What is claimed is as follows:

1. Apparatus for uniformly heat-developing an extended-length strip ofimage-exposed radiation-sensitive heat-developable sheet material andcomprising in combination, porous plate heating means for supplyingheated air at low flow rates uniformly over at least one side of asegment of said strip, drive means for advancing said strip past saidheating means at a constant rate just sufficient to permit fulldevelopment of said strip, retraction means, responsive to the stoppingof said drive means, for the prompt separation of said heating meansfrom close proximity to said segment, cooling means for cooling saidstrip promptly after full development and for cooling said segmentpromptly after said separation, and delay means for briefly delaying theadvancement of said strip after again bringing said heating means intoclose proximity with said segment.

2. Apparatus of claim 1 wherein said porous plate heating means includesmeans for supplying heated air over both sides of said Segment.

3. Method of uniformly developing an extended-length strip ofimage-exposed radiation-sensitive heat-developable sheet materialcomprising advancing said strip, during periods of movement thereof, atconstant full-development rate through a zone of uniformly heated airobtained from porous plate heating means closely adjacent at least oneside of a segment of said strip while continuously cooling said strippromptly after said full development, and, in the event of cessation ofmovement of the advancing strip, promptly retracting said heating meansfrom closely adjacent said strip and simultaneously cooling saidsegment, and thereafter and prior to again initiating the advancing ofsaid strip, returning said heating means to said closely adjacentposition and delaying said advancing for a short time suflicient tobring said segment to its previous point in the heat-development cycle.

References Cited UNITED STATES PATENTS 1,517,434 12/1924 Kluever 2193692,532,032 11/1950 Offen 341S5 X 2,668,701 2/1954 Dietrich 2633 3,084,4894/1963 Seefiuth 156497 X 3,311,525 3/1967 Fanuzzi et al. 1564973,382,789 5/1968 Barker 219--388 X JOSEPH V. TRUHE, Primary Examiner P.W. GOWDEY, Assistant Examiner US. Cl. X.R.

